This invention relates to a semiconductor memory device, and more particularly to a semiconductor memory device having a circuit which functions as a sense amplifier for reading-out of data and also functions as a drive circuit for writing-in of data.
A semiconductor memory device, generally, comprises memory cells in which data are stored, switching transistors coupled to the memory cells, sense amplifiers for reading data out of the memory cells, pairs of bit lines through which data are transferred, word lines through which address signals are applied to the switching transistors, drive circuits for writing data in the memory cells, pairs of data lines through which data are transferred from outside, and so on.
In the case where data are read out of the memory cells in the above-stated semiconductor memory device, an address signal is first applied through a word line to a switching transistor so that a selected memory cell is electrically coupled to a bit line, and data stored in the memory cell appears between a pair of bit lines as a difference of electric potential. Such a minute amplitude of the electric potential due to the read-out data is then amplified by a sense amplifier. After such amplification is carried out sufficiently, the amplified electric potential is readout through a data line to an input/output circuit.
On the other hand, in the case where data is written in a memory cell, data to be written is applied to a drive circuit and a pair of data lines are driven by the drive circuit so that the data to be written is transferred to a memory cell, and stored in the memory cell.
Upon the data writing-in operation, sense amplifiers are in an OFF state, while upon the data reading-out operation, drive circuits are in an OFF state. In other words, when a drive circuit is operating, sense amplifiers are not operated and when a sense amplifier is operating, drive circuits are not operated.
As explained above, a conventional semiconductor memory device has sense amplifiers and drive circuits separately.